System and method for inactivation of infectious pancreatic necrosis virus (IPNV) using medium pressure ultraviolet (UV) light

ABSTRACT

A method and a system is provided for inactivation of Infectious Pancreatic Necrosis Virus (IPNV) comprising illuminating a liquid containing IPNV with a lamp emitting a continuous broad band of ultraviolet (UV) light. The UV lamp may be “tuned” to optimize IPNV inactivation. The lamp may be a medium pressure UV lamp that emits UV light having wavelength between 260-400 nm and preferably, between 260-300 nm. The pressure of the lamp may be greater than 1.6 bar, 3 bar and preferably is 7 bar. The lamp may be composed of PS (synthetic quartz).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Application of PCT InternationalApplication No. PCT/IL2014/050269, International Filing Date Mar. 13,2014, claiming priority of U.S. Provisional Patent Application No.61/788,477, filed Mar. 15, 2013 which is hereby incorporated byreference.

BACKGROUND

Infectious Pancreatic Necrosis Virus (IPNV) is a common contaminant inwater and other liquids in fish farms and is suspected of depletingpopulations of salmon species, such as, Norwegian and Chilean salmon.Ultraviolet (UV) light may be used to disinfect contaminated liquid toinactivate IPNV and thus, reduce the risk of illness. To effectivelydecontaminate liquid, IPNV may be inactivated to a degree greater thanor equal to a log value of 3 (≧99.9% inactivation) by radiating with astandard low pressure UV lamp at a wavelength of 254 nm and applying atleast a UV dose of around 250 mJ/cm². Since the UV dose needed forinactivation is relatively high, standard UV lamps use relatively highamounts of electricity to achieve effective decontamination.

SUMMARY

Embodiments of the invention provide a system, device and method forusing a UV lamp “tuned” to optimize IPNV inactivation. In tests carriedout according to embodiments of the invention, lamps having a wavelengthabove 260 nanometers (nm) and/or below 245 nm were found to inactivateIPNV, e.g., between 3 and 70 times more than UV light at 254 nm or moreaccurately at 253.7 nm. The value of 254 nm, as used herein refers tothe current commonly used industrial LP lamps, which emit at thewavelength of 253.7 nm. Water transmission is better in the high range(e.g. above 260 nm) than the low range (e.g. below 245 nm). Further,polychromatic (medium pressure) UV lamps substantially in a wavelengthrange between 260 and 400 nm were discovered to inactivate IPNV usingsignificantly less UV light or UV dose than monochromatic (low pressure)UV lamps emitting in 253.7 nm.

In some embodiments of the invention, a liquid containing IPNV may beilluminated with a spectrally optimized medium pressure UV light in a UVdose level of less than approximately 50% compared to a UV dose level ofa low pressure lamp emitting at 253.7 nm to produce the same level oflog inactivation of IPNV. Accordingly, spectrally optimized mediumpressure lamp requires less electricity to produce the same level ofinactivation level. The lower UV dose level the less electricityrequired. Optimized IPNV customized lamps are lamps customized anddesigned based on the response sensitivity of the IPN virus. Based onthe response sensitivity of the IPN virus, higher pressure optimized MPlamps may contribute more to a cumulative intensity than the lowerpressure MP lamp. Embodiments of the invention include a MP lamp withpressure higher than 1.6 bar and preferably, higher than 4 or 5 bar soas to match the spectral response of the IPN virus to UV light.

In some embodiments, a UV lamp “tuned” to optimize IPNV inactivation maybe a medium pressure polychromatic UV lamp that emits UV lightsubstantially in a wavelength range of between 260 and 400 nm. In someembodiments, the UV lamp may be a medium pressure UV lamp that emits UVlight substantially in a wavelength range of between 260 and 300 nm. The“tuned” medium pressure polychromatic UV lamp may have a pressure above1.6 bar, for example above 3 bar, above 5 bar, above 6 bar etc. In otherembodiments, the UV lamp may be a monochromatic lamp that emits UV lighthaving a single wavelength in the range of 260-400 nm and preferably, inthe range of 260-300 nm.

In some embodiments, a UV lamp “tuned” to optimize IPNV inactivation maybe a medium pressure polychromatic UV lamp that emits UV lightsubstantially in a wavelength range of between 200 and 245 nm. In someembodiments, the UV lamp may be a medium pressure UV lamp that emits UVlight substantially in a wavelength range of between 200 and 220 nm. The“tuned” medium pressure polychromatic UV lamp may have a pressure above1.6 bar, for example above 3 bar, above 5 bar, above 6 bar etc. In otherembodiments, the UV lamp may be a monochromatic lamp that emits UV lighthaving a single wavelength in the range of 200-245 nm and preferably, inthe range of 200-220 nm.

Both polychromatic and monochromatic UV lamp in both the upper and lowerwavelength ranges are referred to herein as “IPN customized UV lamp”.The IPN customized UV lamps according to embodiments of the inventionmay be composed of pure silica synthetic quartz (PS)

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIGS. 1 and 2 schematically illustrate systems for disinfecting a liquidcontaining in accordance with embodiments of the invention;

FIG. 3 schematically illustrates a system for determining the biologicalresponse of IPNV to UV light in accordance with embodiments of theinvention;

FIG. 4 is a graph that plots the correlation between UV doses for lowand medium pressure UV light, respectively, and the inactivation ofIPNV, in accordance with embodiments of the invention;

FIG. 5 is a graph of the relative spectra of MP UV lamps at differentpressures (e.g., defined by mercury (Hg) bars);

FIG. 6 is a graph of the cumulative intensity of the MP lamps withdifferent pressures;

FIG. 7 is a graph of the IPN spectral response curve, normalized at 254nm;

FIG. 8 is a graph of the cumulative intensity of the MP lamps withdifferent pressures with respect to the IPN spectral response;

FIG. 9 is a summary table listing the total radian power and normalizedradian power of a PS (synthetic quartz) MP lamp and a regular quartz MPlamp; and

FIG. 10 is a graph of the spectra of a PS (synthetic quartz) MP lamp(violet), and the regular quartz (blue).

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DETAILED DESCRIPTION

In the following description, various aspects of the present inventionwill be described. For purposes of explanation, specific configurationsand details are set forth in order to provide a thorough understandingof the present invention. However, it will also be apparent to oneskilled in the art that the present invention may be practiced withoutthe specific details presented herein. Furthermore, well known featuresmay be omitted or simplified in order not to obscure the presentinvention.

Unless specifically stated otherwise, as apparent from the followingdiscussions, it is appreciated that throughout the specificationdiscussions utilizing terms such as “processing,” “computing,”“calculating,” “determining,” or the like, refer to the action and/orprocesses of a computer or computing system, or similar electroniccomputing device, that manipulates and/or transforms data represented asphysical, such as electronic, quantities within the computing system'sregisters and/or memories into other data similarly represented asphysical quantities within the computing system's memories, registers orother such information storage, transmission or display devices.

In some embodiments of the invention, a UV lamp is provided that isoptimized to inactivate IPNV. The UV lamp may be a medium pressure UVlamp that emits UV light substantially in a wavelength range of between260 and 400 nm. In some embodiments, the UV lamp may be a mediumpressure UV lamp that emits UV light substantially in a wavelength rangeof between 260 and 300 nm.

Disinfection systems may irradiate liquids with UV light to reduce orinactivate IPNV. UV lamps may be monochromatic or polychromatic.Monochromatic lamps emit a single wavelength of UV light (for example,280 nanometers (nm)). Throughout the specification, only the commonlyused monochromatic UV lamps that emit at around 254 nm are referred toas “low pressure” (LP) UV lamps. Polychromatic lamps emit multiplewavelengths of UV light, for example, in discrete increments or in acontinuous broad band range (e.g., 260-300 nm), and may be referred toas “medium pressure” (MP) UV lamps. In tests carried out according toembodiments of the invention, optimally customized medium pressure (MP)UV lamps were discovered to inactivate IPNV at significantly greaterrates than standard low pressure (LP) UV lamps configured to emit at253.7 nm. Since the standard LP and customized MP UV lamps inactivateIPNV at different rates, the proper UV intensity and UV exposure time,i.e., the “UV dose,” to decontaminate liquid may differ for each of thelamps.

Measuring the UV dose may be simple for a LP UV lamp (e.g., usingequation D_(CB) defined below) since illumination exposure parametersmay be easily measured for the single wavelength of the monochromatic UVlight. However, this calculation may not be used for polychromaticlight. MP UV lamps, which radiate light over multiple wavelengths,include some wavelengths that actively reduce IPNV, and otherwavelengths that are innocuous or less effective at reducing IPNV. Toaccurately determine the intensity of MP light, the intensity may bemeasured separately at each of the active wavelengths, a generallydifficult task. Currently, only the UV dose to disinfect IPNV with astandard LP UV lamp emitting at 253.7 nm is known, while the UV dose forMP light remains unknown.

To accurately calculate the intensity or UV dose of MP UV light, whichmay be difficult to measure directly, embodiments of the invention maymeasure the UV dose using an LP UV light that gives an equivalent (ofnear equivalent) reduction in microorganisms. Such an MP UV dose may bereferred to as a “reduction equivalent” UV dose (RED) since it is notmeasured, but determined to be equivalent to a LP UV dose that achievesa similar reduction. In one embodiment, to determine the reductionequivalent UV dose for MP radiation of IPNV, the LP UV dose may bemeasured, not for IPNV, but for another control organism, such as, malespecific-2 bacteriophage (MS2). The control organism may have a knowncorrelation between the LP UV doses and the reduction equivalent MP UVdoses used to inactivate the same amounts of the control organism. MS2is inactivated in equivalent UV doses by LP and MP UV light, althoughother control organisms with non-equivalent LP and MP UV doses may alsobe used, as long as the correlation between their LP and MP UV doses isknown or measurable.

In one example, the MP UV dose used to achieve at least a 3 log (≧99.9%)reduction of IPNV was determined to be at least 50% lower compared to aUV dose level of a low pressure lamp emitting at 253.7 nm. (LP UV dose)For comparison, the LP UV dose used to achieve the same reduction inIPNV is approximately 120-246 mJ/cm². Thus, MP lamps provide the samereduction as LP lamps, but with such a significantly smaller UV dose,for example, at least 3-5 times less than LP lamps. Whereas there issubstantially no difference between radiating MS2 with MP and LP UVlight, such a significant difference between radiating IPNV with MP andLP UV light provides a unique and unexpected result.

Reference is made to FIGS. 1 and 2, which schematically illustratesystems 100 and 200 for disinfecting a liquid containing IPNV inaccordance with embodiments of the invention. FIG. 1 includes UV sources102 positioned externally to conduit 101 and FIG. 2 includes UV sources204 positioned internally to conduit 201 within the cavity of thechannel, although any arrangement or combination of internal and/orexternal UV sources may be used.

In FIG. 1, system 100 may include a tube, channel or conduit 101 tocarry flowing liquid to be disinfected and one or more external UVsources 102 to illuminate and to disinfect the liquid within conduit101. Conduit 101 may have an inlet 104 to receive the liquid, and anoutlet 105 to discharge the liquid. Conduit 101 may be made, at leastpartially, of a UV transparent material, such as glass or quartz. System100 may include one or more windows 103 which may be made of UVtransparent material, such as glass or quartz and may, for example, becoated with an anti-deposit layer 125.

UV sources 102 may illuminate or irradiate the liquid when flowing inconduit 101 to inactivate contaminants, such as, IPNV. In someembodiments, the liquid within conduit 101 may act as a waveguide and atleast part of the light, for example, at least half of the emitted UVintensity, may be totally-internally reflected at the interface of theUV-transparent conduit 101 and the surrounding air. UV sources 102 mayinclude one or more IPN customized UV lamp, for example medium pressureUV sources, adapted to emit polychromatic light at multiple (discrete orcontinuous) wavelengths (e.g., in a range throughout the germicidal UVrange and beyond). UV source 104 may comprise pure silica syntheticquartz (PS) UV sources 102 may emit UV light substantially in awavelength range of between 200 and 245 nm. In some embodiments, the UVlamp may be a medium pressure UV lamp that emits UV light substantiallyin a wavelength range of between 200 and 220 nm. The “tuned” mediumpressure polychromatic UV lamp may have a pressure above 1.6 bar, forexample above 3 bar, above 5 bar, above 6 bar etc. In other embodiments,UV source 102 may be a monochromatic lamp that emits UV light having asingle wavelength in the range of 200-245 nm and preferably, in therange of 200-220 nm.

UV sources 102 may be set to emit UV light at a fixed UV dosepredetermined (e.g., in the testing phase of FIG. 3) to inactivate IPNVby an optimal degree. For example, medium pressure UV sources 102 mayilluminate liquid with a UV dose of less than or equal to 80 mJ/cm² toachieve an inactivation of IPNV by at least a 3 log values (99.9%).

In FIG. 2, system 200 may include a conduit 201 to carry flowing liquidto be disinfected and one or more internal UV sources 204 to illuminateand to disinfect the liquid within conduit 101. An illuminating surfaceof each UV source 204 may be substantially perpendicular to alongitudinal axis of symmetry 209 of conduit 201, such that thedirection of illuminating rays is parallel to longitudinal axis ofsymmetry 209. UV source 204 may comprise pure silica synthetic quartz(PS). UV source 204 may emit UV light substantially in a wavelengthrange of between 200 and 245 nm. In some embodiments, the UV lamp may bea medium pressure UV lamp that emits UV light substantially in awavelength range of between 200 and 220 nm. The “tuned” medium pressurepolychromatic UV lamp may have a pressure above 1.6 bar, for exampleabove 3 bar, above 5 bar, above 6 bar etc. In other embodiments, UVsource 102 may be a monochromatic lamp that emits UV light having asingle wavelength in the range of 200-245 nm and preferably, in therange of 200-220 nm. Each UV source 204 may be positioned in aUV-transparent sleeve 202. Sleeve 202 may comprise pure silica syntheticquartz (PS).

In the examples shown in FIGS. 1 and 2, systems 100 and 200 are flowsystems that disinfect liquid as it passes through conduits 101 and 201,respectively, although systems 100 and 200 may be configured in anyother arrangement, such as, a movable UV source passing through a closedcontainer of liquid, a UV source with sufficient surface area toirradiate an entire liquid sample so that no relative motion is neededto expose all the liquid, etc.

Reference is made to FIG. 3, which schematically illustrates abio-dosimetry system 300 for determining the biological response of IPNVto UV light in accordance with embodiments of the invention.

System 300 may include a collimated beam apparatus 302 with a UV source304 and a detector 306 which may include a magnetic stirrer. Samples 308of liquid contaminated with known quantities of microorganisms arepositioned between the UV source 304 and detector 306 to test theirresponse to UV doses of low and/or medium pressure light from UV sources304. Samples 308 may include aliquots of mixed cultures, e.g., placed inPetri dishes, including IPNV and a control organism, such as, MS2,tested separately.

The IPNV sample 308 may be exposed to medium pressure UV source 304 forvarious exposure conditions, such as, various intensities and/orexposure times, and collimated beam apparatus 302 may measure theconcentration of inactive (or active) IPNV for each of these exposures.Collimated beam apparatus 302 may measure the IPNV inactivationconcentrations corresponding to each set of exposure conditions.Exposures conditions above a certain intensity and/or duration mayinactivate IPNV by an optimal concentration (e.g., by at least log 3).Although the exposure conditions are known, the corresponding mediumpressure UV doses may not be easily calculated directly due to thespectral spread of polychromatic light.

To deduce the medium pressure UV doses, the UV dose-response may betested for a control organism with a known correlation between MP and LPUV doses.

For example, MS2 inactivates by substantially similar amounts whenexposed to the same MP and LP UV doses. The control organism may beexposed to a variety of medium pressure UV light to determine acorrelation between IPNV and the control organism inactivationconcentrations for the same exposure settings. The control organism mayalso be exposed to a variety of low pressure UV light to determine acorrelation between LP UV doses and inactivation concentrations of thecontrol organism.

The correlation between IPNV and the control organism inactivationconcentrations for each set of MP exposure conditions may be used tocorrelate MP exposure conditions (linked to IPNV inactivationconcentrations) and LP UV doses or their same reduction equivalent MP UVdoses (linked to MS2 inactivation concentrations). Accordingly, the MPUV doses for IPNV may be deduced from easily measurable LP UV doses forthe control organism. The optimal range of MP UV doses for IPNV mayinclude the subset of those doses that correspond to exposure conditionsthat inactivate IPNV by an optimal degree (e.g., a log 3 reduction).

Tests were conducted according to embodiments of the invention using alow pressure collimated beam apparatus (LP-CBA) including a low pressureUV lamp measuring the LP UV dose-response for the control organism andIPNV (relating LP UV dose to log inactivation) and, similarly, optimizedmedium pressure collimated beam apparatus (MP-CBA) including a mediumpressure UV lamp measuring the MP UV dose-response for the controlorganism and IPNV (relating medium pressure exposure settings to loginactivation). Each of the medium and low pressure CBA tests may bepreformed, in parallel (e.g., the MS2 and IPNV samples were exposed tothe same light at the same exposure time), for the control organism andIPNV to calculate their UV dose responses to the same exposureconditions. The log-inactivation values of IPNV from the MP-CBA wereinput into the laboratory derived-UV dose-response relationship (CBAtest) of the control organism to estimate the reduction equivalent dose(RED) of IPNV delivered by the MP-CBA.

The UV dose calculation spectral respond tests is based on testsdescribed in A. Lakretz et al. 2010 (Anat Lakretz; Eliora Z. Ron; HadasMamane; Biofouling control in water by various UVC wavelengths anddoses; Biofouling Vol. 26, No. 3, April 2010, (57-267) with slightmodifications as follows: The integrated average irradiance between 200and 300 nm is calculated according to Bolton and Linden (2003) [Bolton JR, Linden K G. 2003. Standardization of methods for fluence (UV dose)determination in bench-scale UV experiments. J Environ Eng ASCE129:209-215] using the spectral incident irradiance obtained from acalibrated spectroradiometer (USB4000, Ocean Optics) placed in the samex, y position as the center of the crystallization dish and at thesurface of the liquid suspension, the water spectral absorbance obtainedvia a UV-Vis spectrophotometer (Secoman Uvikon xs), the reflection atthe sample surface and the measured Petri factor for the dish. The UVinfluence is calculated by multiplying the average irradiance withexposure time. In addition, band-pass (BP) filters placed in thepolychromatic light path will be used to transmit a well-defined band oflight from the polychromatic MP light source at a central wavelength of220, 239, 254, 260 and 280 nm with an average full width at half maximum(FWHM) of 20-27.5 nm and minimum peak transmittance ranges between 12and 15% (Andover Corporation, NH, USA). The transmission curves for theBP filters, were performed with a UV-Vis spectrophotometer (Cary Bio100,Varian, Inc., Palo Alto, Calif., USA) for absorbance measurement,equipped with a 150 mm diameter IS attachment (Diffuse Reflectanceaccessory (DRA)-CA-3330, Labsphere, NH, USA). The filter was placed in aholder at the sample transmission port of the integrating sphere. Theactual average irradiance, to which the IPNV are exposed when thefilters are used, is obtained by multiplying (weighting) the spectralincident irradiance (measured without filters) by the bandwidth at eachwavelength (spectral transmittance in percentage), taking intoconsideration the water spectral absorbance, petri factor and the waterreflection.

Different strains of IPNV, American Type Culture Collection (ATCC)#VR-1318 isolated from Trout and ATCC #VR-1320 isolated from Pike fry(Esox lucius), were tested to demonstrate the common response ofdifferent forms of IPNV to medium pressure UV doses. Both strains ofIPNV were propagated in cell cultures including Blugill Fin cell (BF-2)and Chinook Salmon Embryo cell (CHSE-214) cultures. Cell cultures weregrown in Minimum Essential Medium Eagle (MEM-Eagle) formulations withnon-essential amino acids supplemented with 10% New-born Calf Serum(NBCS), 2 mM L-glutamine, 5% Pen/Strep solution and maintained in a22-24° Celcius (° C.) CO2 free incubator. Confluent cultures wereinfected with IPNV and incubated for 4-6 days at 15-16° C. Onceextensive cytopathic effect (CPE) was evident in the cells, the mediumwas collected, aliquoted and maintained at −70° C. for further use.Cells were seeded in 96 well plates, for CHSE-214 5×10⁴ cells/well andfor BF-2—8×10⁴ cells/well. Virus samples were serially 10 fold dilutedup to 10⁻⁸ dilutions and used to infect cell monolayers with eachdilution assayed in triplicates. Infected cultures were cultivatedMEM-Eagle with non-essential amino acids supplemented with 10% NBCS, 2mM L-glutamine and 20 mM Hepes, at 15-16° C. Four days after infection,cells were fixed (with formaldehyde 2%) and stained for 10 min with 1.5%Genetian violet. 50% Tissue Culture Infective Dose (TCID50) titer wasdetermined, for example, according to methods described in Reed, L. J.,& Muench, H. (1938). L. J. Reed and H. Muench; A Simple Method ofEstimating Fifty Percent Endpoints; The American journal of Hygiene Vol27 May 1938 No. 3 493-497. The control microorganism used was MS2including a culture of male specific-2 bacteriophage (ATCC 155597-B1)and E. coli MS2 bacteriophage host (ATCC 155597). MS2 stocks wereprepared and stored, for example, according to the procedure outlined inthe Ultraviolet Disinfection Guidance Manual 2006 (“ULTRAVIOLETDISINFECTION GUIDANCE MANUAL” EPA 815-D-03-00 7 Apr. 2006.)

The bacteriophage titer was checked once immediately after preparation,and again within 24 hours prior to the experiment. The collimated beamapparatus was operated, for example, according to the procedure outlinedin the Ultraviolet Disinfection Guidance Manual. Germicidal lightintensity and Petri factors were measured using OPHIR UV detector. TheUV transmission (UVT) at 254 nm of the viral suspension was measured bya spectrophotometer in a 1 cm quartz cuvette.

The LP UV dose (namely, the US dose of a law pressure lamp emitting at253.7 nm), D_(CB), may be calculated according to exposure conditions(e.g., measured ultraviolet transmitting (UVT) of the microbialsuspension and UV intensity of low pressure lamp). The LP UV dose,D_(CB), may be calculated separately for each CBA test, for example, asfollows:

$D_{CB} = {E_{i}{P_{f}\left( {1 - R} \right)}\frac{L\left( {1 - 10^{- {ad}}} \right)}{\left( {d - L} \right){ad}\mspace{11mu}{\ln(10)}}t}$where:

-   -   D_(CB)=UV dose (mJ/cm²)    -   E_(i)=Average UV irradiance (measured before and after        irradiating the sample) (milliwatts (mW)/cm²)    -   P_(f)=Petri factor (unit-less)    -   R=Reflectance at the air-water interface at the irradiating        wavelength (e.g., 254 nm) (unit-less)    -   L=Distance from the lamp centerline to the suspension surface        (cm)    -   d=Depth of the suspension (cm)    -   a=UV absorption coefficient (base 10) of the suspension at the        irradiating wavelength e.g., 254 nm) (cm⁻¹)    -   t=Exposure time (seconds)

LP UV doses were tested in a range of 0-120 mJ/cm² (0, 20, 40, 60, 80,100, 120, mJ/cm²) for MS2 bacteriophage and 0-250 mJ/cm² (0, 30, 60,120, 250 mJ/cm²) for IPNV. The UV lamp used in the LP-CBA was a 15 watt(W) low-pressure germicidal lamp (emitting at 253.7 nm) and the UV lampused in the MP-CBA was a 1 kilowatt (kW) optimized medium-pressure IPVcustomized lamp. The samples were illuminated using two lamp powers:100% and 25%. 20 ml samples of each viral suspension were illuminatedwith LP-CBA and with MP-CBA in Petri dishes (of 50 cm² surface area, 1cm sample depth) with slow stirring. The IPNV suspension was illuminatedand kept on ice during testing.

The samples were illuminated with the maximum dose to test for possibleharmful effect of the solution to the IPNV. IPNV was added to thesamples immediately after the illumination in the same concentration asadded to the non-UV illumination sample. These samples are referred toas “medium with IPNV” in tables 1-3. Samples without IPNV wereilluminated with the maximum dose to test for possible harmful effect ofthe solution to the cells. These samples are referred to as “medium w/oIPNV” in tables 1-3.

The concentration of each of the samples was determined using an MS2enumeration procedure (e.g., the Pour Plate method) and IPNV plaqueassay/end point titration procedure. The log inactivation may becomputed, for example, as follows:log 10(No/N)where:

-   -   No=Concentration of microorganisms prior to UV light exposure.    -   N=Concentration of microorganisms present after UV light        exposure

The experimental results were computed as a UV dose to log inactivationfunction, and a trend line equation was determined for each LP-CBAexperiment.

The reduction equivalent UV dose value of MP-CBA was determined bycomparing the MS2 bacteriophage's log inactivation achieved by theLP-CBA to the equal log inactivation achieved by the MP-CBA underspecific condition (MP-UV exposure time, suspensions UVT at 254 nm, UVlamp power, etc.). The RED value required for inactive IPNV wasdetermined by comparing the MS2 bacteriophage's MP-UV exposure time(with specific known RED) to MP-UV exposure time of IPNV under specificexposure conditions.

Reference is made to FIG. 4, which is a graph that plots correlationsbetween UV doses and the inactivation of IPNV, in accordance withembodiments of the invention. FIG. 4 shows results for low pressure UVdoses (listed in table 1) The results for low pressure UV doses (in FIG.4) are from tests conducted in accordance with embodiments of theinvention and from literature data (e.g., H. Liltved et al.; Highresistance of fish pathogenic viruses to UV irradiation and ozonatedseawater; Aquacultural Engineering 34 (2006) 72-82).

Table 1 lists results of the IPNV inactivation by UV light irradiatedwith low pressure (LP) lamps. IPNV inactivation results are measured fortwo strains of IPNV, ATCC no. VR1318 (isolated from Trout) and ATCC#VR-1320 (isolated from Pike fry), in two independent tests, “run 1” and“run 2,” to verify results. Only samples with >25 PFU/ml may beconsidered viable. Disinfection may be considered optimal for a loginactivation greater than or equal to 3.

TABLE 1 LP lamp UV dose (in mJ/cm2) for IPNV inactivation LP UV ATCC no.VR1318 ATCC no. VR1320 dose Run I Run II Run I Run II (mJ/cm²) Log.Inact. Log. Inact. Log. Inact. Log. Inact. 0 0.00 0.00 0.00 0.00 30 0.760.72 1.00 0.84 60 0.85 1.36 1.25 1.40 120 2.11 2.10 2.25 2.40 2502.60 >5.2* >3.7* >3.5* Medium with −0.08 NA 0.29 NA IPNV Medium w/o NANA 0.00 0.00 IPNV *Invalidated values

In tests conducted in accordance with embodiments of the invention, noharmful effect to the cell and to the IPNV were detected in theilluminated solutions. No significant difference was observed betweenthe responses of the two IPNV strains, ATCC no. VR1318 and ATCC#VR-1320, when illuminated with UV light. The optimized MP UV lamp wasfound to be more effective for inactivating IPNV than was the LP UVlamp. In the set of CBA tests performed with the optimized mediumpressure (MP) lamp for achieving an inactivation level of the IPNVbetween 0.2-3.3 logs reduction it was found that the optimized mediumpressure lamp (MP) was more efficient by 2.2-8.6 time relative to the LPlamp

Reference is made to FIG. 5, which is a graph of the relative spectra ofMP UV lamps at different pressures (e.g., defined by mercury (Hg) bars).This figure shows the difference in the relative contributions ofdifferent MP Hg UV lamps to the UV effect on IPN. Contributing factorsmay be taken into account: (1) Variation of pressure (e.g., measured bymercury (Hg) bar) in MP lamp will cause enhancement of the specificspectral bands and (2) the material of the envelope and (3) thecomposition of the materials in the lamp. (1) Pressure tuning isdiscussed in reference to FIGS. 5, 6 and 8. (2) The material of theenvelope is discussed in reference to FIGS. 9 and 10. A lamp envelopemade of substantially pure silica synthetic quartz which enables highertransparency at 200-230 nm spectral range and by this the lamps emitsmore UV light at the range of 200-240 nm, the amount of light can beabout 9% higher. (3) Changing the lamps internal chemistry e.g. bydoping, may also increase IPN inactivation since the materials of thelamp affect spectral transmission of UV light. For example, the lampsmay be composed of mercury e.g. doped with a metal halide additive suchas Iron Halide. Such doping may cause the lamp to have higher radiatione.g. in the range of 200-230 and 260-300 nm. In addition, someembodiments may further use “electrode-less” lamps to enable moreflexibility in using different lamp chemistry.

Reference is made to FIG. 6, which is a graph of the cumulativeintensity of the MP lamps with different pressures. The upper line showsthe cumulative intensity of a mercury lamp having 7 Hg bars pressure andthe lower line shows the cumulative intensity of a mercury lamp having1.6 Hg bars pressure. The intensities in these figures are normalized.

Reference is made to FIG. 7, which is a graph of the IPN spectralresponse curve, normalized at 254 nm. This graph shows that IPN isinactivated at a minimum around 254 nm. Inactivation increasesexponentially by both raising and lowering the wavelength to higher andlower ranges. At the lower range (below 254 nm), inactivation of IPNincreases by 17 times. At the higher range (above 254 nm), inactivationof IPN increases by 3 times. The higher range may be preferred in someembodiments because of increased water transmission of UV light athigher wavelengths.

For example, IPN is 70% more sensitive in the wavelength of 260 nm, 300%more sensitive in a wavelength of 280 nm and 1700% in a wavelength of220 nm. Accordingly, a lamp may be used that emits UV light above 260 nmso that the needed dose will be 70% lower than one that is using a lampof 254 nm. A UV system according to embodiments of the invention mayinclude a lamp that emits UV light at a wavelength of approximately 220nm to be 1700% more efficient than a system that is based on UV lampemit UV light at a wavelength of 254 nm.

Another important parameter associated with the performance of UV systemis the water transmission to UV light (UVT). Water transmissiondecreases as the wavelength spectrum decreases. For example, for thewater of Ein Gedi illuminated at 220 nm, after 1 cm the amount ofremaining intensity was 35%. At 260 nm, after 1 cm, the amount ofremaining intensity was 90%. That is, 90% of the photons were stillavailable for inactivating the IPN. Accordingly, a higher range ofwavelengths may be preferred.

Reference is made to FIG. 8, which is a graph of the cumulativeintensity of the MP lamps with different pressures with respect to theIPN spectral response. The upper line shows the cumulative intensity ofa mercury lamp having 7 Hg bars pressure and the lower line shows thecumulative intensity of a mercury lamp having 1.6 Hg bars pressure. Asshown in FIG. 6, a higher pressure MP lamp may contribute approximately40% more to the cumulative intensity than the lower pressure MP lamp.Embodiments of the invention include a MP lamp with pressure higher than1.6 bar and preferably, higher than 4 or 5 bar, for example, 7 bar.

Reference is made to FIG. 9, which is a summary table listing the totalradian power and normalized radian power of a PS (synthetic quartz) MPlamp and a regular quartz MP lamp.

Reference is made to FIG. 10, which is a graph of the spectra of a PS(synthetic quartz) MP lamp (violet), and the regular quartz (blue). FIG.10 shows that the difference in the IPN response sensitivity to the200-230 nm wavelength range (TOC(200-230 nm) PS to Reg) may reach up to9%, contributing to the overall cumulative germicidal intensity.Embodiments of the invention may include a lamp composed of pure silicasynthetic quartz. Such a lamp may have a relatively high transparency at200-230 nm spectral range.

Different embodiments are disclosed herein. Features of certainembodiments may be combined with features of other embodiments; thuscertain embodiments may be combinations of features of multipleembodiments.

The foregoing description of the embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. It should be appreciated by persons skilled in the art thatmany modifications, variations, substitutions, changes, and equivalentsare possible in light of the above teaching. It is, therefore, to beunderstood that the appended claims are intended to cover all suchmodifications and changes as fall within the true spirit of theinvention.

What is claimed is:
 1. A method for inactivation of InfectiousPancreatic Necrosis Virus (IPNV) comprising: illuminating a liquidcontaining IPNV with a ultraviolet (UV) light emitted from a mediumpressure mercury UV lamp tuned to optimize IPNV inactivation, whereinthe UV light being substantially in a wavelength range between 260 and400 nm and the UV lamp exhibits a pressure greater than 1.6 bar.
 2. Themethod of claim 1, wherein illuminating the liquid containing the IPNVcomprises illuminating the liquid with a UV dose of less than or equalto 80 mJ/cm² for 99.9% inactivation of the IPNV.
 3. The method of claim1, wherein the pressure of the lamp is greater than 3 bar.
 4. The methodof claim 1, wherein the pressure of the lamp is greater than 6 bar. 5.The method of claim 1, wherein the UV lamp is composed of pure silicasynthetic quartz.
 6. The method of claim 1, wherein the UV lamp is dopedwith a metal halide additive.